"The website has just been shut down by order of public security," Ai told CNN late Wednesday.

The 54-year old, who helped design the iconic Bird's Nest Olympic stadium in Beijing, has endured a difficult relationship with Chinese authorities. Last year he was detained for 81 days and ordered to pay 15 million yuan ($2.38 million) in back taxes officials said he owed through his company, Fake Cultural Development Ltd.

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He paid 8.45 million yuan ($1.3 million) late last year so he could contest the charges. Had he not paid the sum, he said at the time, his wife would have been jailed.

Ai's family and human rights advocates have said they believe the Chinese government is targeting him for his criticism of the regime.

An internationally renowned artist, Ai's works -- often with political undercurrents -- command hundreds of thousands of dollars. His 2010 installation at the Tate Modern in London involved 100 million porcelain sunflower seeds, each one hand-painted by specialists in China, spread on the floor of the museum's large entrance hall.